This invention relates to an apparatus for protecting a rotating machine such as a centrifugal compressor, electric motor, internal combustion engine, and the like, in the event such a machine goes into reverse rotation and, in particular to an apparatus that automatically supplies lubrication to the machine's lubricated components during periods of reverse rotation.
Machines such as centrifugal compressors are able to operate as turbines which, unfortunately, is typically what occurs when there is a check valve failure. Conventionally, the oil pump is coupled directly to the compressor drive motor and will attempt to pull oil out of the compressor bearings and other lubricated components when the machine experiences a reversal in rotation. This, of course, can result in the destruction of the bearings and damage to other machine parts.
In order to provide reverse rotation protection, many manufacturers provide by-pass systems having as many as four check valves to insure that oil is delivered to the machine from the main pump regardless of the direction of rotation of the machine shaft. Independently driven auxiliary pumps are oftentimes provided which take over the lubrication load if the main pump fails or the machine is turning backwards. Even with the use of an auxiliary pump, the main pump will become dry during periods of reverse rotation thus requiring that the main pump be primed prior to once again assuming normal operations.
All protective devices found in the prior art require the use of additional equipment which greatly increases the cost of the machine. In addition, this type of protective equipment can be complex and difficult to maintain. Although providing a margin of safety, the protective equipment can itself fail thereby endangering the machine.